In the field of oil and gas well production, oil wells having low formation pressures require the use of some type of downhole pump located in the production zone for the purpose of actually pumping the oil through production tubing to the surface. One type of downhole pump is driven by a mechanical rod known as a sucker rod which connects from a surface pump drive unit known as a "pump jack" through the production tubing into mechanical connection with the downhole pump. In the use of such sucker rod pump mechanisms for actuating submersible pumps of this type, a known problem is clogging due to sand or other particle accumulation downhole in the pump. Such clogging often requires that the pump be pulled, repaired and cleaned from time to time. In order to do that, it is necessary to remove the production tubing.
Typically, at the time that submersible pump stops operating, the production tubing is "wet" in that it is filled with oil. Removal of the tubing containing the oil is undesirable for several reasons. First of all, the tubing containing the oil is extremely heavy and thus requires very heavy surface equipment to move. Secondly, it is unsafe to remove the tubing in view of possible oil spillage all over the production equipment at the surface since of course, under certain conditions, the spilled oil may be flammable.
One solution is to remove the oil from the production tubing by perforating the production tubing. Perforation requires a workover rig and equipment to actually place an explosive charge downhole in the production tubing in order to burst through the tubing to allow for drainage of the oil. The use of a workover rig as well as the perforation equipment is extremely expensive and takes additional down time. Various tools have been developed to drain or unload the oil prior to removal of the production tubing and the submersible pump. In some types of tubing drains, the actuation is hydraulic and requires the application of extremely high pressure through the production tubing in order to open plugged holes in a hydraulic type of tubing drain. Such hydraulically actuated tubing drains are undesirable because they also may require a workover rig and extremely high pressure pumps. This again adds expense and may cause additional down time.
Mechanically actuated tubing drains are also known. A myriad of different mechanical actuations have been provided for tools which include some type of attempt to unload a string.